Catalytic conversion of hydrocarbons



DeC- 8, 1953 J. w. MOORMAN ETAL 2,662,050

' CATALYTIC CONVERSION oF HYDRocARBoNs original Filed Nov. 29, v194:1

Patented Dec. 8, 1953 CATALYTIC CONVERSION or Y HYDRocARBoNs,

YJoseph W. Moorman, lpine, andk Louis J. Kelly, Tenafly, N. J.,assignors to The M. vW. Kellogg Company, Jersey City, N. J., acorporationv of Delaware continuation ofi-'application serial No.788,905, November 29, 1947. This application March 16, 1949, seriaiNo.81,814 f f i s Claims. (c1. 1256-50) The present invention pertains toimprovements in the regeneration of used catalytic and similar contactmaterials which become spent or inactive during the course of their `usebythe deposition of a combustible deposit' thereon.

More particularly, the invention pertains tov im.v

provements or" rthis character in the catalytic conversion ofhydrocarbons by a continuous cyclic process wherein solid particles of acatalytic material and vapors ofthe hydrocarbons undergoing conversionare contacted in a conversion zone, spent catalyst particles areseparated from the vaporous conversion products, and

thereafter regenerated for reuse by contacting them with anoxygen-containing gas under suit-- able conditions to cause combustionofthe cari bonaceous deposit thereon. y 1 n Heretofore, variousprocesses have been-proposed for effecting regeneration operations ofthis type. Because or" the .highly exothermic char` acter of thecombustion reaction involvedfand 'the sensitivity of the catalyticmaterials at high temperatures, the provision of ,a satisfactoryregeneration process has been attended with many diculties. Furthermore,conversion reactions of this type are necessarily practiced commer-rciallyV in units of considerable size and capacity, and accordingly theproblem of minimizing the size and cost of the equipment necessary is ofoutstanding importance.

The primary object of the presentinvention is the provision of aregeneration processY wherein the temperature of the regenerationoperation and rate of combustion may be readily and satis,- factorilymaintained within desired limits, and one which may be practicedinapparatus substantially reduced in size and consequent cost oftemperature in a cooling zone extraneous of the The quantity of cooledre-. cycled catalyst necessary in this instance is dependent upon itstemperature, and decreases with decrease invtemperature of the cooledrecycled catalyst stream. However, in the application ofl llowerlimitfor the extent of cooling of the re-A i construction compared to thenecessary apparatus 5 in procedures heretofore proposed.

Prior to the present invention, it has beenpro` posed to effect thevregeneration of a spent'powgdei-ed or nicely-divided cracking catalyst,and:v

similar materials, by a procedure involving suspending the catalystparticles in an oxygen-containing `gas andpassing the suspension througha regeneration zone under conditions adapted to cause combustion of thedeactivating deposit of.

carbonaceous material. It has been further proposed, in connection withthis method, to control' the temperature Voi the regeneration zone byrec 2 thereto after cooling this portion to a suitable regenerationzone.

this previously proposed method a lower-temperature limit to suchcooling and consequent minimum amount of recycle necessary has beenrecog -nized and established, this lower limit being based upon therecognition that combustion of the carbonaceous deposit will not occurbelow the igni-4 tion temperature, and accordingly the lattertemperature has been established as the practical cycled catalyststream.

The present invention involved the discovery thatV by the maintenance ofcertain speciedj` conditions inV the regeneration zone the cooled streamof catalyst particles introducedfor temperature control in theregeneration zone may be cooled to a relatively low temperature,suitably belowthe ignition temperature of the carbonaceous deposit,Without subcooling of the regeneration zone to a point when combustionwould either cease or proceed at an unsatisfactorily low rate.- Theprinciples Aunderlying the invention may 'be applied in variouslmodifications involving the maintenance oi the required temperaturecontrol of the regeneration reaction by (a) coolinga stream of recycledregenerated catalyst, (b) I t coolingva portion ory all of the stream ofspent catalyst to be regenerated, or (c) a combinationof (a) and (b). Inthe practice of the process in all modifications, an oxygen-containinggas is passed upwardly through the particles of ycata- Y lytic materialin the regeneration zone-at a Velocity sufliciently low to cause arelatively densev and concentrated catalyst phase to form in the"regeneration vzone and at a sufficiently high ve locity to produce ahigh degree of turbulenceof cyclinga p'ortionpfr the regeneratedcatalyst the'particles in the dense phase, with a conse-A quentmaintenance of a substantially uniform-f temperature throughout'thedense phase.

VVarious lother specific features, objects, and

advantages -of our invention will be apparent from the followingdetailed description of illusj trative examples of its practice, givenin lconnection with the appended drawing, wherein:

Fig, lis afdiagrammatic illustration ofa s uit-l able arrangement ofapparatus and process ow for the practice of the invention as applied tothe catalytic conversion of high boiling hydrocarbons to low boilinghydrocarbons within the motor fuel boiling range.

Fig. 2 is a sectional view taken along line II-II of Fig. 1.

Fig. 3 is a diagrammatic illustration of a modied form of apparatus forthe practice of the embodiment of the invention involving the cooling ofa recycled stream of regenerated catalyst.v

Following the process ow illustrated in the drawing, a suitable feedstock, for example, a high boiling hydrocarbon fraction such as areduced petroleum crude, gas oil, or the like, is introduced throughline l by pump 2 into heating coils 3 in furnace s wherein it isvaporized and heated t a temperature approximating that required for thesubsequent conversion operation. nthe case of a reduced crudechargingstock a portion of the feed as discharged from the furnace willremain unvaporized. Steam may be suitably in troduced into the furnacecoil at intermediate points through lines to facilitate vaporization,and sufficient pressure is maintained in the furnace oil outlet toprevent coking of the coil. From furnace s the heated charge passes bytransfer line t to the base of a regenerated catalyst standpipe l, orother suitable source of active catalytic material. From standpipe a hotactive catalyst is introduced at a rate controlled by valve 8 into thefeed mixture, the heat oontent of the regenerated catalyst stream beingsuiiicient to vaporize the oil, provide the heat of cracking bysuperheating the vapors and to discharge the products from the reactorat the desired end conversion temperature, for example about 950 F. lnthe case of a reduced crude charging stock, the vaporization of the oilat this point includes a partial decomposition or cracking of thisnon-volatile component of the feed. Additional steam may suitably beintroduced through line s tofform a gaseous suspension with the catalystdischarged through valve 8. The mixture of catalyst particles and vaporspasses through line le into inlet H into the lower part of reactor i2.Reactor l2 is a vessel in the form of a cylinder or other suitable shapehaving a relatively great cross-sectional area compared to thecross-sectional area of the vapor inlet line l0, and these relativeproportions cause a correspending reduction in the velocity of thevapors after their passage from inlet line l). into the reactor l2. Thevelocity of the vapors in reactor l2 preferably is maintained withinsuch limits as to produce therein a highly turbulent and concentrated ordense phase of the catalyst, similar to the condition maintained in zoneA of the regenerator. However, any conditions adapted to producesuitable contact between the catalytic particles and the vaporsundergoing conversion may be utilized in the conversion Zone withreference to the practiceof the present invention.

The dense turbulent catalyst phase (zone A) extendsl only partiallyY upthe reactor, the upper horizontal level thereof being indicated-bydotted line I3. Zone B, the reactor space above this level i3,constitutes a catalyst-vapor disengaging space, a relatively smallproportion of the total catalyst introduced being carried out overheadwith the vaporous conversion products from zone B through vapor outletline lil. Unused or spent catalyst. suitably is withdrawn from theconversion zone by-a catalystwithdrawal pas- '4 sageway I5 openingdirectly into the dense catalyst phase in Zone A. The relativecross-sectional areas of catalyst outlet i5 and reactor l2 are shown byFig. 2. A suitable inert gas such as steam is introduced in the lowerportion of the catalyst withdrawal passageway l5 through line IS todisplace or strip hydrocarbon vapors mixed or entrained with theseparated catalyst and to maintain the catalyst therein in an aeratednowable condition. Catalyst is withdrawn from passageway i5 in twostreams through catalyst standpipes Ii and I8 to which an inert aeratingmedium is supplied by means of suitable inlet lines (not illustrated)distributed at suitable intervals along their length to maintain thecatalyst flowing therethrough in a dense but readily ovvable state.

The vaporous conversion products containing a relatively smallproportion of the total catalyst fed to the reactor, thatV is an amountof the order of about l5 per cent or less, pass overhead from zone Bthrough outlet lli to a suitable gas-solid separating system. Thisseparating system may consist of any one of various available means forseparating the suspended catalyst, and returning it to the system. Thecatalystthus recovered may be returned directly to the reactor, oroptionally to the stripping Zone in catalyst outlet I5. As shown, thissystem comprises a plurality ofcyclone separators l and 20 arranged inseries, in each of which a portion of the catalyst is separated from thevaporsk and withdrawn through the lower hopper, the separated vapors:being withdrawn overhead and passed to the subsequent separating stage.The catalyst is w1thdrawn from the hoppers through tailpipes 20 and 2lwhich Vpreferably extend as indicated ,into the reactor' ashort distancebelow the upper j level of the dense catalyst phase.

Tailpipes 20 and 2l likewisemay be suitably provided with inlet linesdistributed at suitable intervals along their; length for introducing anaerating medium thereto to maintain the catalyst passing therethrough ina flowable condition. The vaporous conversion products Withdrawn fromthe final cyclone through linek? are passed to a suitable productsrecovery system such as a fractionating tower or the like, wherein theproducts are separated into the desired fractions, such as gasoline,fuel oil and cycle oil. The small amount of catalyst remaining in thevapors withdrawn through line 22 may be recovered by partiallycondensing these vapors, thereby concentrating this residual catalyst inthe heavy boiling condensate which may be recycled to the reactorthrough feed line l, as described in Belchetz Patent No. 2,374,073.

Iny appended rfable I there is given an illustratlve example of suitabledimensions for reactor l2 and operating conditions or the conv-ersion ofa reduced crude petroleum oil over a powdered alumina-silica type ofcracking catalyst of the activated clay Super-Filtrol variety, into lowboiling constituents consisting of a large v proportion of low boilinghydrocarbons within the. gasoline boiling range and characterized bytheir high octane value. In this particular case the reactor wasdesigned to process 16,000 bbls/ day of a MidfCcntinent reduced crudehaving a gravity of 23 degrees A. P. I. to produce the followingproducts in the yields indicated:

l0# R. V. l. gasoline vol. 42.5 No. 3 heating oil; vol. 11.7Y Heavy gasoil vol. 32.8 No. 5 fuel oil vol. 7.2

Excess butane vol., 5.5,

Dry gas wgt; 6.5 Coke wgt. 4.2

' TABLE I Reduced crude oil feed, bbls./day 16,000 Steam feed, wt. basedon oil feed 10 Reactor dimensions:

(a) Zone A-ht.ft 18 Zone A-dia.ft 19.5 (b) Zone B-ht.-ft 8 ZoneB--ht.-ft 19.5 Feed wt. ratio of catalyst to oil 7.511 Oil-vapor mixturetemperature (fro-1n furnace outlet), F 900 Regenerated catalysttemperature (standpipe 7), F 1050 Catalyst average concentration, Y.

(a) Zone A, lbs/cu. ft 15.7 (b) Zone B, lbs/cu. ft 1.0 to 1.5 (c)Catalyst draw-off line l5, lbs./

ou. ft 18.5 (d) Vapor line 22, grains/cu. ft 6 Vapor Velocity, f

(a) Zone A, ft./sec 1.5 (b) Zone B, ft./sec 2.06 Oil contact time(average), seconds 10 Catalyst Contact time (a V e r a g e) seconds 156Ratio of weight of oil fed/hr. to Wt. of catalyst in Zone A 3.09 Reactorvapor outlet temperature (Zone B), "F 945 Reactor pressure,

(a) Inlet to Zone A, lbs/sq. in.

gauge 10.0 (b) Outlet from Zone B, lbs/sq. in.

gauge 8.0

Referring now to the regeneration stage of the cyclic operation, thespent catalyst is preferably passed to the regenerator in two separatestreams withdrawnl through catalyst standpipes Il and I8, one of thesestreams being cooled while the other is passed to the regeneratorwithout cooling. A suitable oxygen-containing gas such as airv issupplied to the regenerator by any suitable means such as air compressor23 through manifold line 2l. The air necessary for regeneration may besupplied to the regenerator in several streams, the main quantity of airbeing supplied through line 34 leading to the base of the regenerator.The remaining air may be supplied through lines 25 and 23 to which linesspent catalyst is introduced by catalyst standpipes l'l and I0 atsuitable rates regulated by valves 23 and 2li. In place of anoxygen-containing gas an inert fluid conveying medium such assteam,f1"lue gas or the like, may be supplied to lines 25 and 25. Thegaseous suspension of spent catalyst in line 25 is carried through asuitable cooler or heat exchanger 29 wherein it is cooled to arelatively low temperature, Ypreferably below the ignition temperatureof the carbonaceous deposit, and then passes therefrom through outletline 3 lr into the base of the regenerator. A suitable cooling medium iscirculated to exchanger 29 through lines 30. The gaseous suspension ofcatalyst in line 26 is passed directly to the lower portion of theregenerator Without cooling. Alternatively, all of the spent catalystmay be passed by line 25 through exchanger 29 and the total streamcooled to a somewhat higher temperature corresponding to that resultingfrom mixing the streams in lines 3l and 26. greatly preferred, however,since the flexibility ofA control is greatly enhancedV bydiverting asuit- The use of two lines as shown is` 6 able amount from one stream tothe other as required. f

The quantity of .regenerating fluid introduced into the regenerator ismaintained Within such limits that the upward velocity of the gasesthrough the regenerator is such as to produce a highly concentrated ordense phase of the catalystand one which is also highly turbulent. Theupper level for this dense phase zone A is indicated by dotted line 35and the physical lcharacteristics ofV this phase are similar to those ofdense phase zone `A present in the reactor. y

Zone B', the, space-in the regenerator vabove level 35, similar to zoneB, constitutes a catalystvapor disengaging space, this zone preferablyextending a sufficient distance down from outlet 36 that onlyr a`relatively small portion of the total catalyst introduced is carried outoverhead with the'flue gas from zone B through outlet line 35.Regenerated catalyst is suitably withdrawn from the regeneration zone bya catalyst withdrawal passageway 3l opening directly into the densecatalyst phase in zone A. A suitable aerating and stripping medium suchas steam is supplied to passageway 3l by line 39 in suiiicient amount tostrip the withdrawn regenerated catalyst from entrainedoxygen-containing gas and maintain the body' of catalyst therein in adense but readily owable condition. From passageway or Vcompartment 3lspent catalyst is forwarded by catalyst standpipe 'l to the conversionstage as previously described. v

Catalyst contained in the :due gas suspension Withdrawn overhead throughline 36 may be recovered in any suitable arrangement of gas-solidrseparators, such as cyclones, Cottrell precipitators or the like, andthe recovered catalyst returned without substantial cooling of thisstream to the regenerator through line 38 or any convenient point in thesystem such as reactor I2.

Illustrating suitable operating conditions maintained inv theregeneration pursuant to the present invention, appended iTable IIconsists of a tabulation of regeneration stage conditions correspondingto an operation in the conversion stage as given in Table I.

" Table Il is on the basis of no temperature control duty beingperformed by the catalyst withdrawn overhead through line 36, as forexample, when this catalyst is returned through line V33 atsubstantially the same temperature as withdrawn, or is forwarded to somepart of the system other than the regeneration zone, or is negligible inamount. rTable IV given hereafter illustrates theV application or"the'invention when the stream of catalyst circulated by wayl of lines 36and 33 is utilized to effect a substantial degree of temperature controlduty.

TABLE II Regenerator dimensions: Y

(a) Zone A htP-it 4 '7 Zone A dia. ft 80.5 un l.zone B' straft 1s Y`Zone B diaft 30.5 Spent catalyst-lbsL/hr .1,617,355

Cooled spent catalyst (line 25) 1bs./hr 1,294,420

Spent catalyst (line 25) lbs/hr 322,935 Temperature cooled yspentcatalyst f (line 3|) F 785 to '740 Temperature spent catalyst (line 2B)"F 940 to 985 Temperature regeneration zone, F 1050 Catalyst averageconcentration,

.,(a) Zone Af,.lbs./cu. ft 4Av` 14.8

`accanto high velocity to produce a highdegree of 'turbulence of thecatalytic particles comprised in the dense phase with theconsequentmaintenance of a substantially uniform temperature therein. Inaddition, the catalyst is introduced to said dense phase afterprecooling to a temperature substantially lower than the substantiallyuniform temperature maintained in the regeneration zone. The precooledstream of oatalystfentering the regenerator may suitably be cooled to atemperature below the ignition temperature ofI the carbonaceous depositthereon vwithout resulting in a subcooling of the regeneration zone to apoint at which combustion would either cease or proceed at anunsatisfactorily low rate.

The range of upward gas velocities through the regeneration zone adaptedto produce the required highly turbulent dense catalyst phase in thiszone is dependent upon such physical characteristics as the particlesize and density of the catalyst particles employed and may be readilydetermined for any particular choice or" catalyst or contact agentexperimentally. ln the case of a powdered or finely-divided crackingcatalyst such as the activated clay Super Filtrol conn sisting largelyof particles of mixed sizes smaller than 100 microns, the preferredrange resides within 0.5 to 6.0 ft./second and preferably within themore restricted range of 1.0 to 3.0 ft./second.

A general advantage flowing through the practice of the invention is thereduction in the quantity of catalyst circulated through the heatexchanger in order to accomplish the desired temperature control. Afurther highly important advantage is the reduction in the quantity ofcatalyst cooled and recycled to the regeneration zone with consequentimportant savings with respect to cost of circulating this catalyst andreduction in the size and cost of the equipment including theregeneration vessel and auxiliary lines.

It is to be understood that the examples described in the foregoing areillustrative only and the scope of the invention is not limited exceptas required by the claims appended hereto. This application is acontinuation of our prior and copending application Serial No. 788,95,fled November 29, 194'?, and now abandoned.

We claim:

l. A process for the catalytic cracking ci heavy residual oilscontaining a substantial portion of constituents unvaporizable withoutdecomposition to form lower boiling hydrocarbons in the motor fuelboiling range which comprises passing a stream of said residual oilupward through a cracking zone at a velocity limited to form a denseturbulent bed of catalytic material, introducing a stream oi hotregenerated catalyst While said catalyst is at substantiallyregenerating temperature into said stream of oil while said oil is at anactive cracking temperature but not higher than about 900 and a portionof which is in the liquid phase, the amount and temperature of thecatalyst so introduced being suiiicient to heat said oil above 95:0o F.and partially decompose the unvaporizable constituents contained thereinto thereby form a relatively dry suspension of oil vapors and cataiyst,maintaining the oil vapors in contact with the catalyst thus suspendedtherein within said cra-ching zone for a period sufficient to crack:substantial proportion thereof into motor fuel constituents,continuously separating a stream of finely-divided catalyst containingsolid combustible deposits from the oil vapors by withdrawing directlyfrom said vdense bed of catalytic material,- thereafter fracof oxidizinggas upwardly through said zone at a velocity limited 'to form a dense,turbulent bed of catalytic material and oxidizing gas in the bottomsection of `said regenerating zone, burning combustible deposits fromthe iinely-divided catalyst within said regenerating zone to therebyheat said catalyst to a temperature above the temperature maintained insaid cracking zone but below the deactivation temperature of saidcatalyst, the density and turbulence of the catalytic material Withinsaid regenerating zone being suiiicient to maintain a substantiallyuniform temperature throughout the regenerating zone, continuouslywithdrawing a stream of regenerated catalyst directly from said densebed of catalytic material of the regenerating zone and continuouslyreturning said catalyst to said oil stream while at substantially itsregenerating temperature.

2. In the process defined by claim l, the further improvement in theregeneration of the catalytic material whioh comprises cooling a portionof the hot regenerated catalyst withdrawn from the regenerating zone toa temperature lower than the ignition temperature of the combustibledeposits and substantially lower than said uniform temperaturemaintained in the regenerating zone and returning the cooled catalyst tothe dense turbulent bed of catalytic material in the regenerating zone,whereby the combustion of the solid combustible material is continuouslymaintained at a substantially uniform temperature not in excess of themaximum safe regeneration temperature.

3. A process for the catalytic cracking of heavy residual oilscontaining a substantial portion of constituents unvaporizable withoutdecomposition to form lower boiling hydrocarbons in the motor fuelboiling range which comprises passing a stream ofv said residual oilthrough a cracking zone, introducing a stream of hot regeneratedcatalyst while said catalyst is at substantially regeneratingtemperature into said stream of oil while said oil is at a temperatureof about 900 F., the amount and temperature of the catalyst sointroduced being suiiicient to heat said oil above 900 F. and partiallydecompose the unvaporizable constituents contained therein to therebyform a relatively dry suspension of oil vapors and catalyst, maintainingthe oil vapors in contact with the catalyst thus suspended thereinwithin said cracking zone for a period suicient to crack at least 30 percent thereof into motor fuel constituents, continuously separating astream of finely-divided catalyst containing solid combustible depositsfrom the oil vapors, thereafter fractionating 'the oil vapors tosegregate a motor fuel fraction therefrom, continuously passing a streamof said catalyst separated from said oil vapors into a regeneratingzone, passing a stream of oxidizing gas upwardly through said zone at avelocity limited to form a dense, turbun lent bed of catalytic materialand oxidizing gas in the bottom section of said regenerating zone,burning combustible deposits from the finelydivided catalyst within saidregenerating zone to thereby heat said catalyst to a temperature abovethe temperature maintained in said cracking zone but below thedeactivation temperature of said catalyst, the density and turbulence ofthe vReferenees Cite 'iin the le of this patent UNITED STATES PATENTSNumber Name Date Belchetz Aug. 19, 1941 Scheineman Dec. 28, 1943Scheineman Feb. 8, 1944 Conn May 23, 1944 YHemi-ninger Nov. '7, 1944Tyson Aug. 14, 1945 Martin Aug. 27, 1946 Tyson June 3, 1947

1. A PROCESS FOR THE CATALYTIC CRACKING OF HEAVY RESIDUAL OILSCONTAINING A SUBSTANTIAL PORTION OF CONSTITUENTS UNVAPORIZABLE WITHOUTDECOPOSITION TO FORM LOWER BOILING HYDROCARBONS IN THE MOTOR FUELBOILING RANGE WHICH COMPRISES PASSING A STREAM OF SAID RESIDUAL OILUPWARD THROUGH A CRACKING ZONE AT A VELOCITY LIMITED TO FORM A DENSETURBULENT BED OF CATALYTIC MATERIAL, INTORDUCING A STREAM OF HOTREGENERATED CATALYST WHILE SAID CATALYST IS AT SUBSTANTIALLYREGENERATING TEMPERATURE INTO SAID STREAM OF OIL WHILE SAID OIL IS AT ANACTIVE CRACKING TEMPERATURE BUT WHICH IS IN THAT ABOUT 900* F. AND APORTION OF WHICH IS IN THE LIQUID PHASE, THE AMOUNT AND TEMPERATURE OFTHE CATALYST SO INTRODUCED BEING SUFFICIENT TO HEAT SAID OIL ABOVE 900*F. AND PARTIALLY DECOMPOSE THE UNVAPORIZABLE CONSTITUENTS CONTAINEDTHEREIN TO THEREBY FORM A RELATIVELY DRY SUSPENSION OF OIL VAPORS ANDCATALYST, MAINTAINING THE OIL VAPORS IN CONTACT WITH THE CATALYST THUSSUSPENDED THERERIN WITH SAID CRACKING ZONE FOR A PERIOD SUFFICIENT TOCRACK A SUBSTANTIAL PROPORTION THEREOF INTO MOTOR FUEL CONSTITUENTS,CONTINUOUSLY SEPARATING A STREAM OF FINELY-DIVIDED CATALYST CONTAININGSOLID COMBUSTIBLE DEPOSITS FROM THE OIL VAPORS BY WITHDRAWING DIRECTLYFROM SAID DENSE BED OF CATALYTIC MATERIAL, THEREAFTER FRACTIONATING THEOIL VAPORS TO SEGREGATE A MOTOR FUEL FRACTION THEREFROM, CONTINUOUSLYPASSING A STREAM OF SAID CATALYST SEPARATED FROM SAID OIL VAPORS INTO AREGENERATING ZONE, PASSING A STREAM OF OXIDIZING GAS UPWARDLY THROUGHSAID ZONE AT A VELOCITY LIMITED TO FORM A DENSE, TURBULENT BED OFCATALYST MATERIAL AND OXIDIZING GAS IN THE BOTTOM SECTION OF SAIDREGENERATING ZONE, BURNING COMBUSTIBLE DEPOSITS FROM THE FINELY-DIVIDEDCATALYST WITHIN SAID REGENERATING ZONE TO THEREBY HEAT SAID CATALYST TOA TEMPERATUREABOVE THE TEMPERATURE MAINTAINED IN SAID CRACKING ZONE BUTBELOW THE DEACTIVATION TEMPERATURE OF SAID CATALYST, THE DENSITY ANDTURBULENCE OF THE CATALYTIC MATERIAL WITHIN SAID REGENERATING ZONE BEINGSUFFICIENT TO MAINTAIN A SUBSTANTIALLY UNIFORM TEMPERATURE THROUGHOUTTHE REGENERATING ZONE, CONTINUOUSLY WITHDRAWING A STREAM OF REGENERATEDCATALYST DIRECTLY FROM SAID DENSE BED OF CATALYST MATERIAL OF THEREGENERATING ZONE AND CONTINUOUSLY RETURNING SAID CATALYST TO SAID OILSTREAM WHILE AT SUBSTANTIALLY ITS REGENERATING TEMPERATURE.